Wrapping material having a wax-type coating with spaced protruding particles



Sept. 5, 1967 c. P. BOUGIE 3,340,089l

WRAPPING MATERIAL HAVING A WAX-TYPE COATING WITH SPACED PROTRUDING PARTICLES Filed Nov. 15, 1965 SALT PARTlcLEs I3 I WAX -TYPE COAT! NG /Z HEAT 'l' l SEAL FOOD PRODUCT CLIFFORD P. BOUGIE United States Patent O 3,340,089 WRAPPING MATERIAL HAVING A WAX-TYPE COATING WITH SPACED PROTRUDING PAR- TICLES Clifford P. Bougie, De Pere, Wis., assignor to Milprint, Inc., Milwaukee, Wis., a corporation of Delaware Filed Nov. 15, 1963, Ser. No. 323,948 Claims. (Cl. 117-76) This invention relates to a wrapping material and to packages prepared therefrom. More specifically, this invention relates to a wrapping material comprising a substrate, a heat seala'ble wax-type coating on at least one surface of the substrate, and a dispersed arrangement of hard particles, such as salt, joined to the wax-type coating.

A number of wax-type coatings are used in the packaging art to provide a thermoplastic, heat scalable coating on various substrate materials. These coatings may comprise parafiin waxes, microcrystalline waxes, or mixtures of parain and microcrystalline waxes. Oftentimes, a waxtype coating of the type under consideration will comprise a mixture of paraiiin or microcrystalline wax, or both, with a polymeric film former such as polyethylene, and a blending resin; a plasticizer may also be included in the coating. Various types of additives or modifiers can be incorporated in the coatings to impart or er1- hance specific properties. There may be from about 40 to 95% wax in a wax-type coating of the type with which this invention is to be used.

The waxes to be used in the coatings are petroleum waxes and include iboth parafn and microcrystalline waxes. Parain waxes are derived from light and medium lubricating oil distillates and are mixtures of straight chain or normal hydrocarbons usually ranging .from C to C30 and sometimes higher. Microcrystalline waxes are obtained from heavy lubricating oil distillates and generally range from C30 to C60, In general, the microcrystalline waxes have a melting point of from about 140 F. to 195 F. and the paraffin waxes have a melting point of from about 110 F. to as high as about 185 F., although these ranges are not fixed, and comparatively, the paraffin waxes are hard and brittle whereas the microcrystalline waxes are soft, exible and sticky.

Wax-type coatings of the foregoing nature are often used in the packaging field by reason of their low moisture `vapor transmission rates and may 'be applied to paper or other cellulosic substrates to impart moisture vapor impermeability to the coated material. The coatings can also be heat sealable, exhibit good gloss and transparency and are of relatively low cost. Wax-type coatings can be used in direct contact with food products without affecting their taste and odor. Principally because of these reasons, wax-type coatings enjoy widespread use in packaging applications and they are typically applied to substrates including cellulosic materials such as paper, glassine, cellophane and cellulose acetate and non-cellulosic'materials such as synthetic plastic lms.

However, in spite of their widespread use, many waxtype coated packaging materials as presently known have some undesirable characteristics and the principal object of this invention is to provide an improved packaging material including a substrate having a'Wax-type coating on at least one of its surfaces.

Much of the packaging done today involves the use iig@ Patented Sept. 5, 1967 ice of vacuum packaging techniques wherein a commodity may be enclosed in a heat sealable wrapper, a partial or interrupted heat seal formed between adjacent plies of the wrapper, the wrapped commodity is subjected to subatmospheric or vacuum conditions to pull air from the interior of the package, and then the partial heat seal is completed to enwrap the commodity. Wrapping materials bearing a wax-type coating are used for this type of packaging operation, but it has been found that they present problems when so used. Specifically, when the initial interrupted heat seal is made in a wrapping material bearing a wax-type coating, it has been found that the coating can become soft enough and iiow sufficiently as to sometimes fill in the interruption or opening in the heat seal that is intended to be left clear in order to permit air to escape from the interior of the package.

This problem is accentuated since many wax-type coat-v ings have low heat-sealing temperatures in order to have good flow characteristics so as to form around the packaged commodity. Thus it is not unusual to nd a substantial percentage of the packages made with this type of material by vacuum packaging techniques to be unsatisfactory since a proper vacuum could not 'be applied to the interior of the package. An object of this invention is to provide a wrapping material including a substrate and a wax-type coating wherein the wax-type coating carries a spaced disposition of hard, crystalline materials, such as salt, which serve to maintain separation of adjacent plies of the coated material which have been heat sealed together over a portion of their contiguous surfaces in order that air may escape through the separated area for .the formation of Vacuum packages.

' Many wax-type coatings exhibit the undesirable property of blocking, by which is meant cohesion or adhesion between contiguous layers of similar or dissimiliar materials in roll or sheet form which prevents their being satisfactorily used. Thus a wrapping material including a substrate and a wax-type coating when wound into roll form can exhibit blocking wherein a coated surface will adhere to a coated or `uncoated surface which it contacts and thereby make it diicult to unwind the roll without seriously delaminating the coating. This can also occur in stacks of sheets of the coated material and the ambient temperature and the pressure to which the coated material is subjected will affect the blocking problems. This blocking characteristic of many wax-type coatings has necessitated the use of slip sheets in many instances. A slip sheet may -be interleaved with a waxcoated material when wound into a roll so that the coated surfaces contact the slip sheet rather than adjacent surfaces of the same material and the slip sheet is of a material, or includes a suitable coating, to possess a very low adherency to the wax-type coating; slip sheets may also be interleaved Ibetween stacks of sheets of waxcoated material. The use of a slip sheet, however, results in added expense in producing and using wax-coated material and is therefore a generally undesirable feature. Another object of this invention is to provide a wrapping material including a wax-type coating which further includes hard particles adherent to the wax-type coating surface of a character such as to prevent blocking of the wax-type coated surface to adjacent layers of the same or similar material.

Many foods, when packaged, require the inclusion of additives for use as preservatives in order to obtain a suitable shelf life; as an example, many types of cheeses contain a mold inhibitor ingredient for this purpose. However, most materials of this type are considered food additives and limits of the amount that can be included in the food are established by appropriate governmental bodies or agencies. Some wrapping materials for food products may include food additive materials of this type, thereby decreasing the amount that can be added to the food itself since the amount used in the wrapper must be added to the amount used in the .food and this total cannot exceed the permissible established limit. Therefore, another object of this invention is to improve the vacuum packaging and blocking characteristics of a wax-type coated wrapping material by means of -a non-food additive agent dispersed about the coating so as to enable food additives, especially preservatives, mold inhibitors, etc., to be included injthe food to their permissible quantity limits.

The above problems are particularly acute when packaging cheese since many types of materials used for cheese wrappers require the use of a wax-type coating to achieve satisfactory levels of moisture vapor Ibarrier characteristics, and cheese packagers require a material that is readily heat scalable and can still be efficaciously utilized in vacuum packaging machines; in addition, cheese must generally include suitable amounts of mold inhi-biting ingredients. Thus a truly high quality cheese package requires a combination of characteristics in the wrapping material which is diiiicult to attain with known waxcoated wrapping materi-als and, therefore, a more specic object of this invention is to provide an improved cheese package incorporating a wrapping material having -a waxtype coating.

The foregoing and other more specific objects, such as, for example, the types of materials which can be added to the wax-type coated surface to achieve the foregoing advantages and the determination of the amounts of such materials required to achieve the stated objects, will appear in the description to follow. In the description, reference is made to the accompanying drawings which form a part hereof and in which there is shown, by way of illustration, a specific form in which this invention may be practicedThis form will be described in detail to enable those skilled in the art to practice this invention but it is to be understood that other embodiments of the invention may be used and that changes in the embodiment described herein may be made by those skilled in the art without departing from the true scope of this invention. The scope of the present yinvention is -best delined by the appended claims and limitations set out in the following detailed description need not be taken in a limiting sense except insofar as they may be incorporated in the claims.

By way of summary, this invention provides a Wrapping material including, in combination, a substrate layer, a wax-type coating on at least one surface of said substrate layer, and a dispersed arrangement of hard, crystalline particles joined to and projecting from the wax-coated surface. The preferred hard, crystalline material is salt, sodium chloride, of a defined size range and within a specied amount. The wax-coated surface is only partially covered by the hard, crystalline material so that the wax coating can be used to form heat seals, but there is to be a suicient amount of the crystalline material present on said surface in order to render the surface non-blocking and to provide a wrapping material of improved handling for vacuum packaging methods.

In the drawings:

FIG. 1 is a perspective view of a portion of a sheet of Wrapping material produced in accordance with this invention;

FIG. 2 is an end view of the sheet of wrapping material illustrated in FIG. 1;

FIG. 3 is a top view of a food package wherein cheese enclosed in wrapping material according t-o this invention is to be vacuum packaged;

FIG. 4 is an end view partly in section, taken along 4 the plane of line F4 shown in FIG. 3, looking in the direction of the arrows and showing the package before it has been completely closed; and i FIG. 5 is a view simil-ar to FIG. 4 but on an enlarged scale and showing the package after it has -been completely closed.

FIG. 1 illustrates a portion of a sheet of wrapping material 10 embodying the present invention. The wrapping material 10 includes a substrate 11 comprising a flexible lilm, foil or membrane of sufficient strength for wrapping purposes. Although shown herein as comprising a single layer, the substrate 11 may also consist of more than one layer of the same or dissimilar material joined together, by lamination for example. The substrate can be formed of cellulosic materials such as paper, glassine, cellophane and cellulose acetate or other cellulose esters, and noncellulosic materials, particularly synthetic polymeric films and metal foils. For most packaging uses, the substrate will Ybe from about 1 to 3 mils thick, although other thicknesses can he used.

The substrate 11 carries a wax-type coating 12 on at least one of its surfaces; generally, the substrate can also be coated on both sides or impregnated with the wax-type coating. The wax-type coating 12 is to comprise either entirely paraffin or microcrystalline petroleum wax, a

mixture of parailin fand microcrystalline petroleum waxes,

or a coating having a substantial portion not necessarily a major portion) of paraiiin or microcrystalline petroleum waxes, or both, together with other ingredients such as polymeric ilm-formers and blending resins. Thus the term wax-type coating as used herein and in the claims is intended to refer to these classes of coatings in a generic sense. Wax-type coatings of this general nature are melted and then applied in a molten condition to the substrate by kiss coating, knife coating, squeeze roll coating, dip coating, gravure coating and other conventional coating methods. A wax-type coating or this type is also heat sealable and slightly tacky or sticky at room temperatures, which tackiness increases with elevated temperatures on the order of to 100 F. and above.

The wrapping material as described to this point is conventional inasmuch as it includes known substrates and known wax-type coatings. The novel feature of this invention resides in the particles 13 dispersed about the Waxtype coating 12. These particles 13 are to consist of a hard, crystalline material and are spaced about the coating as individual particles or small agglomerations of particles so that the coating 12 is exposed between the particles. As indicated in FIG. 2, the particles 13 project above the surface of the wax-type coating 12 and are not embedded therein. The particles 13 are to be firmly attached to the coating 12 so that they are not easily removed therefrom. With many coatings, this will require the use of a suitable adhesive binder to hold the particles in place.

Salt, sodium chloride, has been found to be an idealY material for the particles 13 since it possesses the hard crystallinity necessary to impart the desired characteristics described hereinbelow, it is not considered a food additive, and because it has a melting point above the heat sealing or softening temperature of the wax-type coating 12. The salt particles should not be excessively large and should be small enough so that the salt can be kept in suspension when applied to the substrate from a slurry; a particle size ranging from 40 mesh (0.165 inch opening) to 200 mesh (0.0029 inch opening), U.S. Standard Sieve series, has been found effective. As to quantity, the salt should be present at least in the amount of from 1.25 grams per thousand square inches of substrate to 3.5 grams per thousand square inches of substrate. Quantities less than about 1.25 grams per thousand square inches have been found insuiiicient to provide the desired properties to the material. Particles are spaced about the wax coating 12 so that when activated by heat, the coating can ow around the salt particles in order to form a heat seal bond with a contacting surface of another layer of the wrapping material.

A typical packaging use of the wrapping material is illustrated in FIGS. 3-5. Turning first to FIG. 3, a sheet of wrapping material 10 is shown as being wrapped around a stack of cheese slices 14. The sheet of wrapping material is overlapped on the underside of the cheese stack and contacting layers heat sealed together to form the back seam of the package, as indicated at 17 in FIG. 4. The ends of the package are squeezed together and heat seals are formed as indicated in FIG. 3 to join the uppermost layer of wrapping material to the lowermost layer by means of the wax-type coating on each layer. The two heat seals 15 at each end of the package do not join one another and an opening 16 is left between them to provide an area wherein there is no heat seal bond. The heat seal formation is shown in FIG. 4, wherein the wax-type coating 12 of the upper layer of wrapping material contacts the wax-type coating 12 of the lower layer of wrapping material along the heat seals 15 and in these heat seal areas the respective coatings 12 fuse together under the action of heat and pressure to form the heat seals. As stated previously, the wax coatings iiow around the particles 13 attached to each coating 12. However, at the opening 16, the coatings 12 do not heat seal together so that an air passage is formed at each end of the package.

The term heat sealing as used herein is meant to define the property of softening or fusing to form a satisfactory bond when subjected to momentary application of heat and pressure. The temperatures employed are above the softening temperature of the coating, the pressures generally vary between less than one pound to fifty pounds per square inch and the dwell time is normally from a fraction of a second to several seconds.

After being formed in the condition described above, the package is placed in a vacuum chamber wherein the air contained inside the package is withdrawn through the openings 16, heat seals are formed across the openings to complete closure of the package, and the sealed package is removed from the vacuum chamber. Unless the openings 16 can be preserved in the wrapper while the package is in the vacuum chamber and until the package is ready for the final heat seal after being evacuated, it will not be possible to draw the air out of the interior of the package. A difficulty experienced with prior art wrapping materials having a wax-type coating is that the opening often would become entirely closed, or sufhciently closed, to prevent the free passage of air out of the package when the heat seals 15 are initially formed, thereby inhibiting satisfactory application of the vacuum. However, it has been found that the salt particles 13 arranged according to this invention act to preserve the opening between the heat seals so that the packages can be properly evacuated and made ready for final heat sealing and that, consequently, the Wrapping materials of this invention are able to provide improvements over prior art wrapping materials having a wax coating in this type of packaging method.

An appreciation of the advantages of the present invention can be had by reference to the following examples, wherein Example 1 illustrates a wrapping material having a wax coating according to the prior art and Example 2 illustrates the same wrapping material further including the dispersed arrangement of salt particles on the wax coating in accordance with this invention.

Example 1 of substrate, consisting of moisture-proof cellophane desi@ ignated as 210MAD2 that was one mil thick. After the Wax coating had cooled and the wrapping material was ready for use, it was observed that the coating had a definite tacky or sticky feeling. The coating was further tested for blocking by folding a coated sheet so that a coated surface was in contact with another similarly coated surface of the sheet and then pressing the overlapped portions together by moderate hand pressure. The overlapped portions were then separated by hand during which it was observed that the two coated surfaces were quite well bonded to one another, that stripping of the coating from the contacting layers occurred, and that the substrate began to tear. Using the same test procedure, a sheet of the wrapping material was folded with the wax coated surface in contact with an uncoated surface of the substrate. Upon separation, it was observed that there was bonding between the coated surface and the uncoated surface and they could be separated only with some difficulty, and that there was stripping of the coating so that some of it was transferred to the uncoated surface of the substrate; no tearing of the substrate was noted as occurred above when the coated surface was folded in contact with another coated surface. Further experience with the wrapping material indicated that it would block at temperatures above room temperature when subjected to very light pressures. These blocking characteristics are rated as severe and a roll of the material could not be satisfactorily unwound. In order to provide a useful packaging material, it was necessary to use a slip sheet comprising a paper bearing a silicone or other type of release coating, when the wrapping material was wound into a roll for shipment to the packager. A web of the slip sheet had to be wound with a web of the wrapping material so as to be interleaved between adjacent plies of the wrapping material to prevent them from adhering to one another during storage and transfer to the user. Since the slip sheet had to be included on the roll, a usual size roll of the material had about 1800 lineal feet of wrapping material.

When the above wrapping material was used to package cheese by vacuum packaging procedures as described above with reference to FIGS. 3-5 and the interrupted heat seals 15 were formed in the packages, it was found that an appreciable percentage of the packages could not be properly evacuated of air in the vacuum chamber because the wax-type coating tended to close the opening 16. It was estimated that about 5 to 10% of the packages had this defect, which is suicient to substantially increase the cheese packager costs since the defective packages were not suitable for sale without repackaging.

Example 2 A salt slurry was prepared comprising 41.5% salt, 24.5% of a binder consisting of a solution of 20% polyvinyl acetate (Gelva V-l00) and 80% denatured alcohol (ethanol), and the balance ethyl alcohol as a vehicle. Other vehicles, such as methyl, propyl and isopropyl alcohols, and other binders, such as polyamides, acrylic polymeric materials, shellac and ethyl cellulose, can be used, and the salt is preferably present in an amount greater than the amount that would ordinarily dissolve in the vehicle. The particle size of the salt was such that of it went through a 40 mesh screen, 21% of which passed through a 60 mesh screen, 58% through a 100 mesh screen, and 21% through a 200 mesh screen, all U.S. Standard Sieve series. The slurry was agitated to keep the salt in suspension and applied to the wax-coated surface of the same wrapping material described above in EX- ample l. The slurry was applied with a rotogravure coater and the vehicle evaporated by passing the coated web through a drying oven at a speed of 200 ft./min. for a dwell time of about 10 seconds. The finished sheet was as shown in FIG. l and had a multitude of salt particles distributed over the wax coating and joined thereto by means of the binder, polyvinyl acetate. The sheet had a slightly rough feeling on the salt coated surface since the salt particles projected above the wax coating. The coating had a dryfeeling and gave no evidence of tackiness or stickiness when rubbed by hand. The coated material was tested for blocking by folding in the manner explained in Example 1 and it was found that the salt bearing Wax coated surface would not adhere to a superimposed salt bearing wax coated surface as was true in Example 1 when the wrapping sheet was tested without the salt particles. Further, the salt-coated surface would not adhere to a superimposed uncoated surface of the substrate. It was also found that the material of this example, having the salt particles over the wax coating, could be wound into roll form or stacked as sheets without the use of a slip sheet by reason of its improved blocking characteristics. For these reasons, the salt-coated sheet of this example according to this invention exhibited none of the undesirable blocking characteristics shown by the material of Example 1. Thus a usual size roll, of the same size as described in Example 1, was able to incorporatev about 3000 lineal feet `of the wrapping material, as opposed to only 1800 feet of wrapping material that had to be slip sheeted as indicated in Example 1; this provides an additional advantage for the wrapping material of this invention in that it reduces the time consumed in changing rolls on a wrapping machine and, hence, lessens the time during which a wrapping machine need be taken out of production to reload with wrapping material.

When the wrapping material of this example was used to package cheese according to the vacuum technique described above with reference to FIGS. 3-5, it was found that there was no tendency for the packages to close the openings 16 before the package could be properly evacuated of air. The salt particles on thewax coating surfaces, being hard, and projecting from the surfaces, kept the opposed surfaces sutiiciently far apart to provide an eciernt air passage between the heat seals 15, and it was found that the percentage of defective packages due to an inadequate opening almost entirely disappeared so that it can be considered as zero percent or a negligible percentage. Thus the wrapping material of this invention eliminated one of the problems of vacuum packaging associated with conventional wax-coated sheet materials as discussed above in Example 1.

In the preceding examples, the butyl rubber inthe wax coatings was an isobutylene-isoprene copolymer having 0.7% unsaturation, a specific gravity of 0.92 and a Mooney ML-8 at 212 F. in the range of 60 to 80. The I polyethylene had a molecular weight of 6000 'Ihe microcrystalline wax had an ASTM melting point of 140 F., needle penetration of 40 at 77 F., and a Saybolt viscosity of 79 at 200 F. The wax coating formula is exemplary 4and the three ingredients can be varied within a wide range; e.g., the wax can be from 40 to 95%, the rubber from 4 to 35%, and the polyethylene from 2 to 25%. Also, one or more of these ingredients can be omitted or substituted so that the coating can consist entirely of wax or of wax blended with other ingredients. For the purpose of this invention, a wax-type coating is defined as one containing' from about 40 to 100% wax. The wax coating in the examples can be heat sealed at from 80 F. to 250 F., depending on the dwell time and the pressure; at the lower temperatures, an increased dwell time and/ or increased pressure are required. In normal packaging uses, the material is heat sealed with equipment set at/a heat Iseal jaw temperature of 225 F., dwell time of 3/30 second and a jaw pressure of from 20-50 p.s.i.; with these machine conditions the Iactual interfacial temperature in the area 'of the contiguous coatings is in the range of 140 to While salt is shown as the material for the particles to be distributed over the wax surface of a wax-coated substrate the materials of this invention, other materials can also be used. The material for the particles should be hard and crystalline; materials such as starch, talc, and chalk are soft and amorphous and have been found generally unsatisfactory for the present invention and incapa- 'ble ofproviding the vacuum packaging advantages in particular. The particles should also have a suiiiciently high melting point so that they do not melt when the material is heat sealed, i.e., when the wax-type coating is softened or activated by heat. Further, the particles should be a nonfood additive when the wrapping material is used to package food; when used for packaging cheese the particles should be of a material that is considered a non-food additive in accordance with the appropriate standards that have been established by government agencies such as the FDA. Examples of other useful materials include calcium and potassium chlorides; sodium, calcium yand potassium salts of tartaric, lactic, acetic and phosphoric acid; the sugars glucose and sucrose; and organic hard resins having a softening point of 104 C. to 300 C. (ball and ring method).

There has thus been described a wrapping material utilizing a wax-type coated substrate and whichV is further altered in accordance with this invention to achieve novel results, particularly with reference to vacuum packaging capabilities and blocking, not heretofore attainable with this general class of wrapping materials. Is to be understood that it is intended to cover all changes and modifications of the example of this invention herein chosen `for the purpose of illustration which do notV constitute 'a departure from the spirit and scope of this invention.

I claim:

1. In a wrapping material of the type including a substrate of flexible packaging material `and a wax-type coating on at least one surface of the substrate, said wax-type coating comprising at least about 40% petroleum wax and being heat scalable, the improvement consisting of a plurality of particles attached to the wax-type coating, said particles comprising hard, crystalline material with a melting point above the heat sealing temperature of the waxtype coating selected from the group consisting of sodium chloride, calcium chloride and potassium chloride; and said particles being arranged to project from the wax-type coating 'and spaced to expose said coating between the particles so that the coating can be heat sealed 2. Wrapping material according to claim 1 wherein the particles are tine enough to pass through 'a 40-mesh screen and Ia major portion are large enough to be retained on a 20D-mesh screen.

3. Wrapping material according to claim 1 further including adhesive binder material joining the particles to the Wax-type coating. Y

4. Wrapping material according to claim 1 wherein the particles attached to the wax-type coating are sodium chloride salt particles arranged to project from the wax-type coating and spaced to expose said coating between the saltparticles so that the coating can be heat sealed.

5. Wrapping material according to claim 4 wherein there is at least 1.25 grams of salt per 1,000 square inches of coated substrate.

6. Wrapping material according to claim 4 wherein the salt particles are ne enough to pass through a 40- mesh screen and a major portion are large enough to be retained on a 20G-mesh screen.

7. Wrapping material according to claim 6 wherein there is at least 1.25 grams of salt per 1,000 square inches of coated substrate.

8. Wrapping material according to claim 4 further including adhesive binder material joining the salt particles to the wax-type coating.

9. Wrapping material according to lclaim 8 there is vat least 1.25 of coated substrate.

10. Wrapping material according to claim 9 wherein the salt particles are fine enough to pass through Ia 40- mesh screen and a major portion are large enough to be retained on a 20G-mesh screen.

wherein grams of s-alt per 1,000 square inches (References on following page) References Cited UNITED STATES PATENTS Prochazka 117-18 Sermattei et a1. 117--158 X Borden et al. 117-157 Bennett 99--179 Weltman et a1 117-9 X James 117-92 X 10 Kepple et al 117-8X Keilsmeier et al 99-178 Smith et al 117-144 Rag-an et al 117-92 X WILLIAM D. MARTIN, Primary Examiner.

HYMAN LORD, Examiner.

R. HUSACK, Assistant Examiner. 

1. IN A WRAPPING MATERIAL OF THE TYPE INCLUDING A SUBSTRATE OF FLEXIBLE PACKAGING MATERIAL AND A WAX-TYPE COATING ON AT LEAST ONE SURFACE OF THE SUBSTRATE, SAID WAX-TYPE COATING COMPRISING AT LEAST ABOUT 40% PETROLEUM WAX AND BEING HEAT SEALABLE, THE IMPROVEMENT CONSISTING OF A PLURALITY OF PARTICLES ATTACHED TO THE WAX-TYPE COATING, SAID PARTICLES COMPRISING HARD, CRYSTALLINE MATERIAL WITH A MELTING POINT ABOVE THE HEAT SEALING TEMPERATURE OF THE WAXTYPE COATING SELECTED FROM THE GROUP CONSISTING OF SODIUM CHLORIDE, CALCIUM CHLORIDE AND POTASSIUM CHLORIDE; AND SAID PARTICLES BEING ARRANGED TO PROJECT FROM THE WAX-TYPE COATING AND SPACED TO EXPOSE SAID COATING BETWEEN THE PARTICLES SO THAT THE COATING CAN BE HEAT SEALED. 